refactor(cli): use the canonical dispatch pattern for alerts and license

[joshrotenberg]

Part of #1049 (Phase 3, CODE-09).

Problem

alerts, license and workflow license were the last enterprise command groups using an in-file dispatch pattern:

#[derive(Debug, Subcommand)]
pub enum AlertsCommands { /* ... */ }

impl AlertsCommands {
    pub async fn execute(&self, config: &Config, /* ... */) -> AnyhowResult<()> {
        let conn_manager = ConnectionManager::new(config.clone());
        // match + handler calls, all in the same file
    }
}

Every other group (database, cluster, node, crdb, logs, module, rbac) uses:

pub async fn handle_x_command(
    conn_mgr: &ConnectionManager,
    profile_name: Option<&str>,
    command: &XCommands,
    output_format: OutputFormat,
    query: Option<&str>,
) -> CliResult<()>

with the enum declared separately and the handler bodies in a *_impl.rs module.

Change

• Moved the three enums into cli/enterprise.rs as EnterpriseAlertsCommands, EnterpriseLicenseCommands and EnterpriseLicenseWorkflowCommands, matching the Enterprise*Commands naming of its neighbours.
• Added alerts_impl.rs, license_impl.rs and license_workflow_impl.rs holding the handler functions.
• alerts.rs, license.rs and license_workflow.rs are now dispatch-only, exposing handle_alerts_command, handle_license_command and handle_license_workflow_command.
• Handlers take &ConnectionManager rather than constructing one from &Config. The workflow handlers, which need the profile list, read it off conn_mgr.config.
• license_workflow_impl.rs imports calculate_days_remaining and bytes_to_gb from license_impl instead of reaching into super::license from a sibling command module.

Behavior

None intended. The clap attributes, subcommand names, aliases, after_help examples and handler bodies all move verbatim. enterprise alerts --help, enterprise license --help and enterprise workflow license --help render the same command lists as before.

Two things were deliberately left alone:

• handle_enterprise_workflow_command still passes None for query to the license workflow (main.rs). That drops the global --query/-q for enterprise workflow license, but it is pre-existing and orthogonal to the dispatch shape.
• license_workflow_impl::license_monitor still calls std::process::exit(1) for --fail-on-warning. That belongs with the exit-code taxonomy work in Automation contract: tracing corrupts -o json, duplicate error line, exit codes, error envelope #1045.

Checks

cargo fmt --all -- --check, cargo clippy --all-targets -- -D warnings and cargo test all pass locally. cargo doc --no-deps --all-features produces only the two pre-existing warnings in cli/enterprise.rs (module :args and a bare cluster URL), unchanged by this diff.

Follow-up

The "add a command" checklist for AGENTS.md, also listed under #1049 Phase 3, is a separate docs-only change and is not in this PR.